对manymany表中记录数的简单计数

Question

class Author(models.Model):
   name = models.CharField(max_length=100)
   age = models.IntegerField()
   friends = models.ManyToManyField('self', blank=True)
class Publisher(models.Model):
   name = models.CharField(max_length=300)
   num_awards = models.IntegerField()
class Book(models.Model):
   isbn = models.CharField(max_length=9)
   name = models.CharField(max_length=300)
   pages = models.IntegerField()
   price = models.DecimalField(max_digits=10, decimal_places=2)
   rating = models.FloatField()
   authors = models.ManyToManyField(Author)
   publisher = models.ForeignKey(Publisher)
   pubdate = models.DateField()
class Store(models.Model):
   name = models.CharField(max_length=300)
   books = models.ManyToManyField(Book)

我想我错过了一些非常明显的东西，但我如何得到在这个多对多表authors = models.ManyToManyField(Author)中创建的记录数量的计数?

Answer 1

查看文档，非常简单:

b = Book.objects.all()[0]
b.authors.count()

更新:

最初的问题是要求数据库中所有作者的列表，而不是寻找每本书的作者列表。

获取数据库中所有作者的列表:

Author.objects.count() ## Returns an integer.